This invention relates to particle collectors and fractionators for both collecting and fractionating particles from a stream of gas. While the instant invention may be used in any application requiring the separation of particulate matter from a gaseous medium, the invention is particularly well suited for separating and fractionating fine particles of pollutants from the ambient atmosphere incident to air sampling tests, as will become apparent hereafter.
Particle collection and fractionating devices are well known in the prior art. Examples of such devices appear in U.S. Pat. Nos. 2,947,164, 3,693,457, 3,823,602, 3,922,905 and 3,938,366.
Ideally, a particle collector and fractionator should be easy to clean and simple in construction, but nonetheless capable of accurately fractionating and effectively collecting a group of gas suspended particles into a large number of discrete categories of aerodynamic diameters. Moreover, when the collector is being used to collect particles of pollutants from the ambient atmosphere, the accuracy of the particle density measurements should not be affected by winds or other forms of air currents. Finally, such a collector should be convenient and simple to operate either by itself, or in conjunction with particle filters or other forms of conventional particle collecting and sampling equipment.
However, none of the particle collectors developed thus far in the prior art appears to possess all of the aforementioned desired features.
For example, while the particle collection and fractionating device disclosed in U.S. Pat. No. 3,823,602 is relatively simple in construction, this device must be inconveniently rotated by an electric motor or other means in order to collect and fractionate particle suspended in a gaseous medium. Furthermore, instead of fractionating the particles into discrete categories of different aerodynamic diameters, this device produces a continuous smear of particles of ever increasing aerodynamic diameters along a single collector strip. Additionally, the particle density measurements of this device are likely to be affected by winds or air currents since this device samples the air from only a single port, which may or may not be properly oriented with respect to wind direction to capture an air sample truly representative of the density of particle pollutants in the ambient atmosphere.
While the particle collection and fractionating device disclosed in U.S. Pat. No. 3,922,905 is both relatively simple in construction and easy to use, it is capable of fractionating the particles into only two categories of aerodynamic size. Moreover, since it samples the air from only a single plane surface, the accuracy particle density measurements of this device are also likely to be affected by the proper or improper orientation of this surface with respect to wind and air currents.
Finally, while the particle collection and fractionating devices disclosed in U.S. Pat. Nos. 2,947,164, 3,693,457 and 3,938,366 are each capable of fractionating the particles into a wide variety of size-categories, each of these devices is relatively complicated in structure, and consequently complicated to disassemble and clean.
Clearly, the foregoing prior art examples illustrate the need for a particle collection and fractionating device which is easy to clean, simple in construction, easy and convenient to use, capable of effectively separating the particles into a large number of aerodynamic size categories, and whose accuracy is completed unaffected by winds or other air currents.